Electron Transport Chain (ETC) + Fermentation

Key Concepts and Processes

• Overview of Cellular Respiration
    - Processes involved: Glycolysis, Krebs Cycle (Citric Acid Cycle), Electron Transport Chain (ETC), and Fermentation.

• During Glycolysis and Krebs Cycle:
    - Productions: $ext{ATP, NADH, FADH}<em>2$   - By-products: $ext{CO}_2$   - Overall Reaction:     $C_6H</em>{12}O_6 + 6O_2 <br>ightarrow 6CO_2 + 6H_2O + ext{Energy}$
      - Questions Raised:
        - Where does water come from in this reaction?
        - Where is the bulk of energy produced?
        - What happens to the NADH and FADH2?

• Final Reaction in Glucose Oxidation:
    - Overall equation:
      $ext{NADH} + ext{FADH}_2 + ext{O}_2 + ext{ADP} + P_i <br>ightarrow ext{NAD}^+ + ext{FAD} + H_2O + ext{ATP}$
      - Key Points:
        - Oxygen is reduced to water.
        - Electrons from $ext{NADH}$ and $ext{FADH}_2$ (which are oxidized) power this reaction.
        - Location of Reaction: This occurs in the mitochondria.

Oxidation and the Electron Transport Chain (ETC)

• NADH Oxidation:
    - Eukaryotes: Occurs in the inner membrane of the mitochondria (cristae).
    - Prokaryotes: Occurs in the plasma membrane.
    - Collective Name: Molecules responsible for oxidation referred to as the Electron Transport Chain (ETC).

• ATP Production:
    - Produced by Oxidative Phosphorylation.

• Mechanism of the Electron Transport Chain:
    - Structure: Composed of proteins embedded in the membrane.
    - Electronegativity: Proteins exhibit differing electronegativities; electrons pass from low to higher electronegativities.
    - Final Electron Acceptor: Oxygen.
    - Key Concept: Difference in electronegativity is crucial for ETC function.

Components of Electron Transport Chain

• Key Molecules:
    - FMN: A nucleotide with a flavin-containing group.
    - Fe•S: Protein with an iron-sulfur group.
    - Cytochrome (Cyt): Protein with a heme group.
    - Ubiquinone (Q): Hydrophobic molecule composed of a carbon ring and isoprene tail; lipid soluble, moves throughout the mitochondrial membrane.

• Protein Structure:
    - All but one protein of the ETC are embedded in the inner membrane of mitochondria.

Chemiosmosis and ATP Synthesis

• Chemiosmotic Theory: Proposed by Peter Mitchell.
    - ATP production is indirect; the primary role of ETC is to create a proton-motive force that drives ATP synthesis by a mitochondrial protein.

• Experiment Overview:
    - Research Question: How are the electron transport chain and ATP production linked?
    - Hypotheses:
      - Chemiosmotic Hypothesis: Linkage is indirect; ETC creates a proton-motive force that drives ATP synthesis.
      - Alternative Hypothesis: Linkage is direct; ETC is associated with enzymes performing substrate-level phosphorylation.

Experimental Setup

• Process:
    1. Produce vesicles and add ATP-synthesizing enzyme and bacteriorhodopsin (a light-driven proton pump).
    2. Illuminate the vesicle to induce proton movement.

• Predictions:
    - Chemiosmotic Hypothesis: ATP will be produced within the vesicle.
    - Alternative Hypothesis: No ATP will be produced.

Experimental Results

• ATP production observed within the vesicle in the absence of the electron transport chain leads to the conclusion that:
    - Confirmed Conclusion: Linkage of electron transport and ATP synthesis is indirect; the movement of protons drives ATP synthesis.

Structural Organization of the Inner Mitochondrial Membrane

• Internal Structure:
    - Vesicles formed from inside-out mitochondrial membrane.
    - Fo Unit: The base of ATP synthase; F1 Unit: The knob.
    - Intermembrane Space and Mitochondrial Matrix are critical areas in proton diffusion.

Summary of Cellular Respiration

• Phases:
    - Glycolysis: 1 molecule of glucose yields:
      - 2 pyruvate, 2 NADH, 2 ATP.
    - Pyruvate Processing: Converts 2 pyruvate to 2 acetyl CoA and produces 2 NADH.
    - Citric Acid Cycle: Each acetyl CoA yields:
      - 6 NADH, 2 FADH2, 2 GTP.
    - Overall Yield:
      - In the mitochondrion, each glucose molecule generates: 8 NADH, 2 FADH2, 2 GTP during oxidation.

Impact of Electron Acceptor on Respiration

• If an electron acceptor (such as oxygen) is present, cellular respiration proceeds through:
    - Glycolysis, Pyruvate Processing, Citric Acid Cycle, Electron Transport, and Oxidative Phosphorylation.

• If no electron acceptor is present, organisms may perform fermentation:
    - Lactic Acid Fermentation (in humans).
    - Alcohol Fermentation (occurs in yeast).

Product Yields from Fermentation

• Lactic Acid Fermentation: Pyruvate accepts electrons from NADH, producing lactate.

• Alcohol Fermentation: Pyruvate converted through acetaldehyde to ethanol.

• Summary of Yields:
    - Glycolysis: 1 glucose yields 2 pyruvate, 2 NADH, and 2 ATP in the cytosol.
    - Mitochondrial Mechanism: 2 pyruvate processes yield 8 NADH, 2 FADH2, and ATP equivalents through GTP.

Conclusions on Metabolic Pathways

• Pathways for Various Biomolecules:
    - Carbohydrates (sugars), Fats (fatty acids), Proteins (amino acids).

• Metabolic flexibility allows cells to utilize various substrates, such as glucose, fatty acids, and amino acids, in energy production and biosynthesis.